Upvote:3
An ESTA is not granted for a specific trip, but is instead valid for 2 years from the date that it's issue. Within that 2 years you are able to enter the US multiple times, with each visit falling under the provisions of the US Visa Waiver Program (VWP).
There is no need to obtain a new ESTA for your return trip unless your original one expires before you enter the US for the return trip, if you obtain a new passport, or if any of the details provided during the ESTA application change (eg, citizenship, criminal record, etc)